1. Field of the Invention
This invention relates to a panel heater for animal use and to a method of manufacturing such a panel heater. Generally, they comprise a body member of slab like shape, the body member comprising an external shell or frame and a heating means embedded within a matrix or quantity of fire retardant material, the fire retardant material being mounted within a shell or frame.
2. Background Information
Before my invention disclosed in British Patent Specification No. GB 2 289 608 (O'Donnell) all known panel heaters of this type were made in a mould and removed from the mould when manufacture was complete. For example, European Specification No. 598 401 (Bernhard) describes a panel heater comprising a zigzag flexible electrical conductor mounted on a grid-like frame, both the conductor and the frame being sandwiched between two layers of fire resistance material, namely, an artificial stone layer and a natural stone slab. This heater is produced in a number of separate moulding stages, thus making it time consuming and relatively expensive to produce. The use of both the grid-like frame upon which the conductor is mounted and the natural stone slab add to the expense of the panel heater.
A further example of this type of panel heater is described in Irish Short Term Patent No. IES 59643 (McGorry). This specification describes a panel heater comprising a body member of slab-like shape, the body member comprising a shell having an outer major surface forming a heat exchange surface, an electrical heating element mounted within the shell and supported by a number of spaced-apart bollards, a matrix of fire retardant material mounted within the shell around both the heating element and the bollards and an insulating panel positioned between the matrix and the base of the shell. However, as this panel is completely produced in a mould and involves a number of moulding steps, the process is very complicated. For example, the shell of the heater described in IES 59643 is moulded in at least four separate stages, each stage involving a curing step. This is very time consuming and therefore makes such a panel heater very expensive to produce. A further problem with the panel heater described in IES 56943 is that it is extremely difficult to inspect both surfaces of the shell before proceeding with the further moulding stages.
Most of the problems with these known panel heaters were solved by the invention of the present applicant, described and claimed in the above mentioned British Patent Specification No. GB 2 289 608. This specification describes a process for producing a panel heater, which comprises securing a plurality of bollards on a base of an open mouthed rectangular box and placing an electric heating element having end connectors around the bollards. The end connectors are engaged within an internal connector housing. A quantity of fire retardant material is cast in the box about the electrical heating elements and the bollards and allowed to set before being covered with an insulating panel. A closing lid is then attached to the open mouthed rectangular box to form the base of the panel heater. This specification also describes a jig for securing the bollards to the base of the open mouthed rectangular box which jig can be removed after casting of the fire retardant material. This invention allowed the panel heaters to be produced simply and cheaply and it has indeed proved to be a most successful and useful panel heater.
Some problems have arisen in the practice with the use of panel heaters manufactured in accordance with the invention of this GB Patent Specification No. 2,289,608 (O'Donnell).
Firstly, quite strangely, it has been discovered that the actual shape of the panel heater, namely, its slab-like shape with vertical sides caused animals and in particular pigs considerable discomfort. This was surprising as there did not seem to be any reason why it should do so. However, the solid vertical sides of the panel heater, did cause some difficulty for the pigs, not alone in getting on top of the panel heater, but in coming off it, in that they tended to damage themselves, either getting on or getting off the panel heater: it caused them some discomfort, but not necessarily serious discomfort. A second problem that was noted was the fact that in certain cases the location of the electrical heating element within the panel heater was not ideal in that in some cases minor damage to the panel by an animal's hoof led to the exposure of the electrical heater element with consequent injury if not death of the animal. It quickly became apparent in use that there was a need to provide a better construction of panel heater that would overcome these problems.
Further it was found important to ensure that any fire retardant material cast in the panel heater, be securely keyed to the shell because during use there were problems in that the fire retardant material filling the shell separated internally from the shell under the continual loading and unloading of the panel heater by the animals using it. This in turn led to cracks and other damage to the shell destroying the structural integrity of the panel. It has however to be emphasised that this happened only after continuous use, if not mis-use.